you've probably figured htis out in 4 weeks, but I don't see a reply so I figured I'd document it for someone else.
A thread is posted to one magazine, while a microblog is posted to the whole fediverse.
To see your threads a user has to be subscribed to the magazine in question (or on some platforms at least one user on the remote instance does), while to see your posts a user has to follow @srasmus@fedia.io
So a new thread is a new lemmy (or Reddit) post, while a post is a new toot/tweet.
A lemmy user can't see the posts to your microblog, a mastodon user won't see your treads unless they "follow" the "user" @askmbin@fedia.io and it looks kind of janky, with every post/reply looking as if the magaize user is re-tooting it.

